The presently disclosed embodiments pertain to a novel imaging member, namely, an electrostatic latent image generating member that can generate an electrostatic latent image through a single step charging process. The embodiments provide a novel way of generating an electrostatic latent image without the need for a photodischarge period that limits the speed with which the image forming apparatus can operate and limits the geometry of the image forming apparatus.
In conventional electrophotographic printing, the charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively photodischarge the surface in accordance therewith. This photodischarge step takes a period of time determined by the transit time of the charge carriers and the required reduction in surface potential. This time is referred to as the photodischarge period. After the photodischarge period, the resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced or printed. The toner image may then be transferred to a substrate or support member (e.g., paper) directly or through the use of an intermediate transfer member, and the image affixed thereto to form a permanent record of the image to be reproduced or printed. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
Thus, it can be seen that current xerographic printing involves multiple steps, such as, charging the photoreceptor; selectively exposing the photoreceptor to light to induce photodischarge, allowing time for photodischarge to occur to create a latent image; developing the latent images, transferring and fusing the developed images; and, erasing and cleaning the photoreceptor. This sequence of steps limits the geometry and space which in turn limits the compactness of the system. Future trends in the industry are focusing on using machines that are smaller and faster. Thus, there is a need to re-design engine architecture to achieve machines that are less limited in compactness, such as for example, a printing apparatus that can create the latent image in a single step during charging.
Moreover, in conventional xerography the transit time of charge carriers after light exposure also limits the speed at which the system can operate. As system speed is increased the time available for photodischarge is reduced and the surface potential reduction is therefore also reduced. To address this issue, new hole transport molecules and imaging member layer designs have been used to reduce the discharge time. However, even the fastest of the newer molecules and designs are limited by the inherent low field transit time after light exposure. To overcome this limitation, it was proposed to eliminate the discharge step altogether and produce a latent image in a single charging step. U.S. patent Ser. No. 12/887,434 to Klenkler et al., filed Sep. 21, 2010 discloses an imaging member that allows for the latent image to be created during the charging process through use of digitally addressable metallic pads arranged as pixels, sandwiched between a thin-film transistor (TFT) backplane and a thin dielectric surface layer, where each pixel pad can individually be selectively isolated or connected to ground through the transistor backplane. A latent electrostatic image can be created on the dielectric surface of the imaging member by selectively grounding the pixel pads in an imagewise fashion while exposing the dielectric surface of the device to a corona source, such as a corotron. The ionized corona gas will be selectively electrostatically attracted to the grounded pixels under the dielectric layer. Thus, the charge acceptance under the scorotron is selectively controlled via the energized backplane. However, such embodiments are complex and thus there remains a desire to achieve a more simpler design that also provides high speed xerography.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrophotographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule” or “electron transport molecules.”